Sekretions

Secretions are substances produced by cells, glands, or organs and released to a target site, surface, lumen, or circulation. They play roles in digestion, lubrication, protection, and communication.

Secretions are often categorized by their destination: endocrine secretions enter the bloodstream (hormones); exocrine secretions are discharged through ducts onto epithelial surfaces or cavities (saliva, gastric juice, sweat, bile).

Secretory mechanisms include merocrine secretion (products released by exocytosis without loss of cytoplasm), apocrine secretion (a portion of the cell's cytoplasm is pinched off), and holocrine secretion (the whole cell disintegrates).

Secretory products include enzymes (amylase, proteases, lipases), mucus, acids, buffers, hormones, sweat, tears, milk, bile, and pheromones. Glands such as salivary, gastric, pancreatic, hepatic, and mammary glands illustrate exocrine secretion; pancreatic islets, pituitary, thyroid illustrate endocrine.

Plants and some microbes also secrete substances such as nectar, essential oils, resins, latex, and secondary metabolites for defense or attraction.

Clinically, secretions are studied for diagnostic value and can reflect health status; abnormal secretions may indicate infection, inflammation, or metabolic disorders.